Langerhans Cells (LC) are members of the dendritic cell family of professional antigen presenting cells, and play a key role in T-cell mediated immune responses in the skin. The principal investigator has developed a series of long term cultured cell lines (designated XS series) derived from neonatal mouse skin, which have characteristics suggesting they may be a useful model to study LC maturation that occurs in vitro as well as in vivo. During antigen-dependent interactions with T-helper cells, their XS cell lines undergo a number of phenotypic and functional changes such as the secretion of IL-1-beta, up regulation of B7-1 and B7-2 molecules, and lose their expression of growth factor receptors, lose their ability to proliferate, adhere to plastic and phagocytose microscopic particles. All of these changes may reflect some of the changes that LC undergo in culture during their maturation. The investigators' central hypothesis is that T-cell activation in vitro and in vivo can be regulated by modulating the terminal maturation of LC. They propose that such studies may reveal strategies to manipulate T-cell inflammatory responses. Their proposed aims are to delineate the important steps of LC maturation during antigen-dependent T-cell maturation. The specific aims are: Aim 1. To characterize the events that occur in LC upon antigen-dependent, T-cell induced maturation. XS cells and FACS purified LC will be co-cultured with antigen specific T-lymphocytes in the presence of appropriate antigen. The XS and LC will then be studied for change in cell surface phenotype, cytokine production (ELISA, RT-PCR and Northern blotting). Reversibility of maturation as well as ultimate fate (apoptosis). They will also study LC terminal maturation during contact hypersensitivity; Aim 2. To study the molecular mechanisms of T-cell dependent terminal maturation. The investigators will study the mechanisms that trigger B7-1 and B7-2 expression, using antibodies to crosslink class II MHC and cytokines. They will also study the relationship between fibronectin metabolism and adhesive and phagocytic capacities; Aim 3. To identify cytokines that prevent or promote the terminal differentiation of LC. An extensive panel of 24 cytokines will be tested for the ability to modulate the terminal differentiation of LC. The investigators will attempt to clone (expression cDNA cloning), the gene encoding the DC maturation inhibitory factors derived from stromal cells (designated NS cells; and Aim 4. To regulate T-cell mediated skin disease by modulating the terminal differentiation of LC. They will attempt to modulate LC terminal maturation in vivo and their capacity to induce allergic contact dermatitis and to produce long term immunologic tolerance.